The present invention is directed to a passive display device particularly useful for signs and reflectors such as house numbers, automobile license plates, door signs, traffic signs, warning signs, advertisements, reflectors for bicycles and automobiles, road markers and light conducting tracks or indicators which are easily recognizable both during the day and night and do not require any external light source.
The recognizability of different signals or displays up to the present time have been accomplished in various ways. For example, in the case of house numbers and automobile license plate numbers as well as door warnings and traffic signals all use a strong contrast for example a bright indication on a dark background. In the case of signs such as traffic signs and warning signs, an application of fluorescent or phosphorescent coatings has been used and the coating will luminesce when irradiated.
In advertising signs, one possibility was to utilize additional illumination such as from gas discharge tubes to create the display. In the case of reflectors such as reflectors which may be used either on automobiles or bicycles, an increased display reflection was obtained by utilizing back scattering elements. For road markers, for example, light guide tracks and lane markers, the display used either back scattering elements or phosphorescent coatings of paint to provide an improvement of the recognizability from direct irradiation.